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Subject: Re: Fast hash key method - Revisited!

Author: Robert Hyatt

Date: 11:18:13 01/14/98

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On January 14, 1998 at 14:04:53, John Bartkiw wrote:

>
>    Just a question for anyone.  I've noticed most people are using a
>table of random numbers to use instead of the actual bitboards.  Can
>someone give me the reasoning for this?  Is it do to the sparseness of
>the bitboards?
>

yes and no.  If you use the bitboards only, you couldn't tell the
difference
between a king on a2 and a pawn on a3 and a king on a3 and a pawn on a2,
which would be a killer.  Random numbers will tend to have about 1/2 of
the bits set to zero, the other half set to 1.  So moving a single piece
affects *lots* of bits, rather than only 2...  to make the hash
distribution
more uniform.

>John.
>
>>
>>The key in seq A would be something like:
>>origKey ^ randTable[white][king][c3] ^
>>          randTable[black][king][c6] ^
>>          randTable[white][king][b2]
>>
>>And for B:
>>origKey ^ randTable[white][king][c1] ^
>>          randTable[black][king][c6] ^
>>          randTable[white][king][b2]
>>



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